Some selected highlights

GO 11113: Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

A composite of HST images of the Kuiper Belt binary, WW31

The Kuiper Belt consists of icy planetoids that orbit the Sun within a broad band
stretching from Neptune's orbit (~30 AU) to distance sof ~50 AU from the Sun
(see David Jewitt's Kuiper
Belt page for details). Over 500 KBOs are currently known out of a population of
perhaps 70,000 objects with diameters exceeding 100 km. Approximately 2% of the known
KBOs are binary (including Pluto, one of the largest known KBOs, regardless of
whether one considers it a planet or not). This is a surprisingly high fraction, given
the difficulties involved in forming such systems and the relative ease with which
they can be disrupted. It remains unclear whether these systems formed from single
KBOs (through collisions or 3-body interactions) as the Kuiper Belt and
the Solar System have evolved,
or whether they represent the final tail of an initial (much larger) population of
primordial binaries. This proposal will use WFPC2 imaging of known KBOs to identify
new binary systems.

Planet formation occurs in circumstellar disks around young stars. Most of the gaseous content of those
disks dissipates in less than 10 million years, leaving dusty debris disks that are detectable
through reflect light at near-infrared and, to a lesser extent, optical wavelengths. The structure
of those disks is affected by massive bodies (i.e. planets and asteroids), which, through
dynamical interactions and resonances, can produce rings and asymmetries. Analysis of the
rangle of morphological structure in these systems provides insight into the distribution
of properties of planetary systems. HST currently provides the only means of achieving
the high-contrast required for the detection of these scattered light disks in the presence of
the bright parent stars.
The present proposal is using NICMOS to target 22 nearby stars that have a strong mid-infrared excess,
based on combining optical, near-infrared and mid-infrared IRAS observations. Most of
the targets are early-type stars, with spectral types ranging from late-B to mid-G.

GO 11192: NICMOS Confirmation of Candidates of the Most Luminous Galaxies at z > 7 231

The history of the Universe in a nutshell..

Current cosmological models predict that the first galaxies started to
form very early in the history of the Universe, at redshifts z > 8. Identifying
individual galaxies at high redshifts clearly offers one means of probing the
details of that formation process. Several recent analyses have succeeded in
finding several galaxies at redshifts in the range 6 < z < 7. Those galaxies
have relatively high luminosities and corresponding high masses, exceeding
1010 MSun. This suggests that these are relatively
mature systems, whose progenitors should be readily detectable at redshifts
z > 7. However, deep pencil-beam surveys that reach those limits have
faield to find any plausible "dropout" candidates.
The present program aims to probe this issue by using NICMOS to
target a number of z > 7 candidates from the GOODS wide-field IR survey.
The NIC3 F110W and F160W observations can both confirm whether these
really are high redshift galaxies, and probe the detailed structure of
any such systems.

GO 11544: The Dynamical Legacy of Star Formation

The central regions of the young star cluster, IC 348

General indications are that the overwhleming majority of stars in the Galactic disk
form within clusters. Understanding the cluster environment is therefore important
to understanding how most stars - and any associated planetary systems - form and
evolve. Star-star interactions can lead to truncation of nascent disks, disruption of binary
systems and even ejection from the cluster. The present program aims to investigate
these issues by surveying the young star cluster, IC 348, with WFPC2, and combining the
present set of observations with data from past cycles. Accurate relative astrometry will
enable measurement of the relative stellar motions, and hence the cluster velocity
dispersion, as well as premitting the identification of any stars with unusually high
motions. In addition, these new WFPC2 images will push observations to fainter limits,
potentially revealing new substellar-mass cluster members.